1. Field of the Invention
The invention relates to an electronic measuring device, in particular a meter, including at least one A/D converter receiving measurement signals, and a digital signal processing device connected downstream of the A/D converter, the signal processing device having a correction element with a first stored reference value and a resulting first correction factor for compensating for any measurement error in an upstream signal detection, the A/D converter can receive a test voltage as a measurement signal, and the correction element can produce a new correction factor when there is a difference between the reference value and the value of the test voltage.
Such a measuring device is disclosed in German Published, Non-Prosecuted Patent Application DE 26 30 959 A1, corresponding to Published French Patent Application 2 357 907.
International Patent Publication WO 95/10781 discloses an electronic measuring device in which digitized measurement signals are monitored for a measurement error. If a measurement error occurs, a correction pulse is produced, so that the measurement error is compensated for. That measuring device is preferably used for measuring consumption, in particular for a meter.
If an A/D converter is used for such an electronic measuring device, the converter generally requires a reference voltage source. That is also the case if a sigma-delta modulator (.SIGMA..DELTA. modulator) is used. The reference voltage must meet high requirements, since the accuracy of the measuring device is directly dependent on the reference voltage. High measurement accuracy therefore also requires a precise reference voltage, which is very complicated to produce, and it is not necessarily possible to ensure operational reliability.
2. Summary of the Invention
It is accordingly an object of the invention to provide an electronic measuring device, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which exhibits high measurement accuracy while at the same time compensating for influences on the measurements.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electronic measuring device, comprising at least one A/D converter for receiving measurement signals including a test voltage having a value; a reference voltage source connected to the at least one A/D converter for operation; and a digital signal processing device connected downstream of the at least one A/D converter; the signal processing device having a correction element with a first stored reference value and a resulting first correction factor for compensating for any measurement error in an upstream signal detection, the correction element producing a new correction factor when a difference exists between the first reference value and the value of the test voltage, and the new correction factor is the first correction factor corrected corresponding to or on the basis of the difference, or it is an additional correction factor.
In this manner, the entire measurement path for signal detection is based on the test voltage. This means that, for example, systematic errors, in particular the temperature response of the A/D converter or an effect of an upstream multiplexer, are detected and compensated for. This produces dynamic measurement error compensation, as it were.
It is advantageous if the first correction factor adapted or corrected on the basis of the difference is used as the new correction factor. This makes simple dynamic adaptation of the correction factor possible. If necessary, the original value can also be saved in a further memory as a precaution.
As an alternative to this, an additional correction factor can be used as the new correction factor. This enables the original setting and the dynamic or instantaneous factor to be separated. The separate correction factor is responsible for dynamic adaptation during operation.
In accordance with another feature of the invention, there is provided a device for cyclically checking the difference or producing the new correction factor. This means that the measurement accuracy is continuously checked and adapted with respect to a changed reference voltage or other influences on the measurements. In this case, the cycle times can be prescribed depending on the measurement accuracy desired.
In accordance with a further feature of the invention, the measurement signals are current and voltage signals, and the signal processing device includes a device for metering electrical power consumption. This constitutes a preferred application of the invention. The measuring device is then used as a meter.
In accordance with an added feature of the invention, the A/D converter has a sigma-delta modulator (.SIGMA..DELTA. modulator). This produces favorable interaction in terms of a precise processing of measured values.
In accordance with a concomitant feature of the invention, the signal processing device produces an error signal whenever the difference exceeds a prescribed limit value. This provides additional error monitoring.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electronic measuring device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.